Imaging devices of planar, external drum and internal drum design, such as photoplotters and scanners, are known in the art. Scanners function by illuminating the test sample with an unmodulated optical beam and capturing the reflected or transmitted light after it leaves the copy. The transmitted or reflected optical signals are received by a detector and recorded.
Photoplotters are used in the field of graphic arts and the fabrication of printed circuit boards. Planar imaging systems, such as are disclosed and claimed in U.S. Pat. No. 4,851,656 and incorporated herein by reference, are types of imaging systems which have a planar surface for receiving a substrate or media. An optical exposure head is located on a movable gantry apparatus and is rastered above the media during exposure.
Internal drum devices have a cylindrical surface portion to receive the media. An optical beam generator emits a modulated optical feed beam onto a parabolic spinning mirror, and the mirror reflects the beam onto the media. As the mirror spins, the reflected imaging beam advances across the media surface from one side edge of the surface to an other side edge thereof, exposing a sequence of pixels which together form a scan line perpendicular to the axis of the drum. The spinning mirror is mounted on a carriage which moves along a spar parallel to the axis of the drum and perpendicular to the scan line. The carriage moves continuously so that the imaging process is helical along the cylinder. The rotating imaging beam advances across the surface area of the drum in this manner until the entire image is exposed to the media.
In the internal drum system, the optical imaging beam is exposed to air turbulence as it travels from the spinning mirror to the imaging surface of the drum. The air turbulence adversely effects the quality of the scanned image. It is known that the greater the beam travels the greater the likelihood of the adverse effects of the air turbulence and therefore, it is desirable for the radius of the drum to be as small as possible. However, the width and flexibility of the media plate and the clearance necessary to load the plate onto the drum limits how small the radius of the drum may be.
The smaller internal drum imaging devices expose plates of media typically having dimensions of 21".times.24" for 4-up format printing and plates of 32".times.42" for plates of 8-up media printing format. The widths of the smaller plates permit the radius of the internal drum to be sufficiently small and yet provide sufficient space between the drum and the spar to easily load and unload the plates of media onto and off of the drum.
The dimensions of the larger media plates for larger imaging devices capable of exposing media of large (i.e. 16-up) format printing are approximately 52" by 68". The handling and loading of the larger media onto the internal drum is difficult and requires the assistance of two individuals. However, the increased diameter of the internal drums of imaging devices for scanning the larger media substantially increases the imaging beams susceptibility to air turbulence within the exposure chamber of the internal drum.
Accordingly, it is an object of the present invention to provide a media feed apparatus for an imaging device that reduces the cycle time to load and remove large plates of media onto or from an internal drum.
It is another object to provide a media feed apparatus for an imaging device that reduces the difficulty to feed a large sheet of media onto the internal drum.
It is a further object to provide a media feed apparatus for an imaging device that permits one individual to load the large plates of media onto the internal drum of the imaging device.
It is yet another object to provide a media feed apparatus for an imaging device that accurately and remotely positions a media plate onto the internal drum of the imaging device.
It is still a further object to provide a media feed apparatus for an imaging device that reduces the effects of air turbulence the imaging beam.